The stems and leaves of Stevia rebaudiana contain a group of diterpene glycosides, called “steviol glycosides”, some of which are up to 400 times sweeter than table sugar (sucrose), depending upon the sucrose equivalence (defined below) required for a given food, beverage, or other comestible. Many steviol glycosides have been isolated and identified, and include, but are not limited to: rebaudioside A (“Reb A” or “RA”), rebaudioside B (“Reb B” or “RB”), stevioside (“STV”), steviol bioside (“STB”), rebaudiosides C, D, E, and F, rubusoside, and dulcoside A. All of these compounds are sweet; however, at commonly used sucrose equivalencies, all but pure rebaudioside A also have a bitter in-mouth taste (taste while a test substance is in the buccal cavity) and bitter aftertaste (lingering taste after swallowing or expectoration of the test substance). Reb A has a clean sweet taste and, at purities greater than 99% and at commonly used sucrose equivalencies, has none of the in-mouth bitterness and bitter aftertaste associated with the other steviol glycosides. Reb A can be produced in various purities using, inter alia, the process described by Jackson in U.S. patent application Ser. No. 11/252,430 (U.S. published application no. 2006/0083838, issued as U.S. Pat. No. 7,923,552) which is fully incorporated hereby by reference).
Blends of various purities of rebaudioside A can be used as sweeteners. The higher the RA content of a sweetener, the more expensive the sweetener is. Blending various purities of rebaudioside A produces sweeteners at selling prices corresponding to the RA purity of the ingredients: the higher the RA purity of the ingredients, the higher the selling price of the blended sweetener.
Liquid sweeteners are required for beverage production and for many food products at commercial scale. Some countries have a strong preference for liquid table top sweeteners, e.g., South American and Asian countries. Non-caloric and low caloric natural, “high intensity” sweeteners are in high demand for use in non-caloric or reduced-caloric foods and beverages, but widespread adoption of sweeteners containing RA and/or STV has been hindered by two factors: (1) the solubility of Reb A and STV are proportional to the Reb A or STV content of the sweetener, and (2) the sensory profile of steviol glycosides differs significantly from that of sucrose in, inter alia, slow temporal decay of sweetness, and “thin” mouth feel; moreover, purities of Reb A lower than RA97 and any purity of STV typically have a bitter aftertaste at sucrose equivalencies used in foods and beverages. This means that the more soluble a known Reb A or STV sweetener is, the worse it can taste. The problems with solubility of known Reb A and STV compositions are described have been disclosed in the art (Prakash et al, “Development of rebiana, a natural, non-caloric sweetener”, Food and Chemical Toxicology”, 46:7, Suppl., July 2008, Pages S75-S82.
RA50 (RA50 is a product comprising >50% RA, and >95% total steviol glycosides) powder dissolves easily in water at 25° C., but the solubility of RA97 (RA97 is a high purity RA product comprising >97% RA) under the same conditions is only 0.8%. The higher the purity Reb A or STV, the faster it precipitates out of solution. A concentration of RA97 any higher than 0.8% rapidly precipitates out of solution. High purity STV also exhibits a similar phenomenon of very low solubility, and rapid precipitation out of solution. Two illustrations show the solubility barrier now existing in the art of Reb A and STV sweeteners. For soft drink dispensing equipment designed for an sucrose equivalent (SE—a measure of sweetness) of 12, using a syrup that has an SE of 0.8 would increase the volume of the syrup by a factor of 15 to reach an SE of 12 in a dispensed beverage. Increasing the volume of syrup by a factor of 15 would be uneconomic, and also impractical for small volume goods. In countries that prefer liquid table top non-sucrose (aka “artificial”) sweeteners, two drops of liquid sweetener provide the sweetness of a teaspoon of sugar (4 grams). However, two drops (200 μL) of RA97 sweetener (assuming RA97 is 300× sweeter than sucrose) only provides an SE of 0.48 grams of sucrose rather than an SE of 4 grams of sucrose. Known Reb A-based liquid sweeteners have failed commercially because they cannot provide adequate sucrose equivalencies. Ideally, if the solubility problem were overcome, the liquid sweetener could be dried and used as a dry (powdered, agglomerated, or granulated) sweetener.
The sensory profile problem that has impaired commercial acceptance of Reb A and STV sweeteners is typically addressed by using masking agents if lower purity (and more soluble) Reb A or STV is used, or by using higher purity Reb A and STV in much lower volume, as a flavor rather than as a sweetener. Ideally, overcoming the solubility problem would also provide a natural sweetener with an improved sensory profile.